Circular Polarization Structure for Depth Sensing Speckle Reduction
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Solution Overview
Problem
Current depth sensing camera systems using laser illumination face issues with wavelength instability due to optical feedback and speckle noise, which limit the accuracy of depth detection.
Innovation Solution
The implementation of a circular polarization structure, including a quarter wave plate and linear polarizer, to convert linearly polarized light from the laser to circularly polarized light, reducing speckle patterns and eliminating reflection-induced instability, thereby enhancing depth accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linearly polarized light from the laser is used for illumination, then the illumination intensity is sufficient, but speckle noise is generated that limits depth detection accuracy
Solution Approach 1:
The patent changes the polarization state parameter of the illumination light from linear to circular by introducing a quarter-wave plate. This parameter change transforms the coherent linearly polarized light into circularly polarized light, which reduces speckle noise generation while maintaining sufficient illumination intensity for depth detection.
2Ease of operation
If optical elements are placed in the laser illumination path, then the illumination pattern can be formed, but optical feedback destabilizes the laser wavelength
Solution Approach 1:
The patent introduces a circular polarization structure (quarter-wave plate) as an intermediary element between the laser and the illumination pattern formation optics. This intermediary converts the linearly polarized laser light to circularly polarized light, which prevents optical feedback from destabilizing the laser wavelength while still allowing the diffractive optical element to form the required illumination pattern.
3Measurement precision
If circular polarization structure is added to reduce speckle noise, then depth accuracy improves, but device complexity increases
Solution Approach 1:
The patent segments the optical system into distinct functional modules: the circular polarization structure (quarter-wave plate) as a separate component, the diffractive optical element for pattern formation, and the illumination/detection optics. This segmentation allows the speckle reduction function to be added without fundamentally redesigning the entire optical system, thereby limiting the increase in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces speckle noise by a factor of the square root of 2, improving depth accuracy and stability, and preventing laser wavelength instability caused by reflections.
Implementation Method 1
The structure creates circularly polarized illumination radiation emanating from the illumination radiation source
Implementation Method 2
A linear polarization element receives the collimated illumination radiation and provides polarized radiation to a quarter wave plate
Implementation Method 3
optics used with such systems may destabilize the wavelength due to optical feedback from the optics in the system
Implementation Method 4
when the coherent light from the laser is re-imaged to the detector, there is noise in the form of a speckle pattern
Data Source
AI summary
A depth image capture device uses a circular polarization structure positioned at the output of an illumination radiation source, such as a diode laser. A linear polarization element receives the collimated illumination radiation and provides polarized radiation to a quarter wave plate. Radiation exits the quarter wave plate as circularly polarized radiation and is provided to a diffractive optical element outputting a pattern to illuminate a target. A detector receives a reflection of the output pattern from the target.